Method of ascending casting in casting cavities, and casting mould or mould part for use when carrying out the method

ABSTRACT

A method of ascending casting in a casting cavity where filling from the bottom results in a region of reduced pressure formed during the cooling in which solidification can be expected to take place last. The region is post-fed with molten material from a shortest possible feeding duct. By doing this, the consumption of casting metal is reduced, because it is no longer necessary to use a surplus of molten material to keep the bottom ingate open for feeding purposes and the consumption of mold material is also reduced because it is no longer necessary to adapt the mold to accommodate surplus molten material.

TECHNICAL FIELD

The present invention relates to a method of casting with pouring fromthe bottom (ascending casting) with post-feeding and to a casting mould(or mould part), said method and casting mould being of the kind inwhich regions of reduced pressure formed during the cooling are fed withmelt.

BACKGROUND ART

It is commonly known that metals, when cooled from the liquid to thesolid state, undergo a reduction in volume, a so-called thermalcontraction. In casting moulds, in which a non-uniform heat distributionreigns in the mould cavity after the pouring, and in which for thisreason all parts of the casting do not solidify at the same time, thiscauses the parts of the casting solidifying last to give off liquidmetal to compensate for the contraction of the parts of the castinghaving solidified earlier, possibly leading to faults in the casting,commonly known as “shrinkage holes” appearing in the form of thepresence in the surface of the casting, or cavities (macroscopic ormicroscopic holes) within the casting. In order to avoid these castingfaults, the skilled person can take recourse to a series of expedients,of which the most common is the use of feeding reservoirs, i.e. cavitiesin the mould being filled with metal during the pouring and having suchdimensions that the metal in them solidifies later than the parts of thecasting solidifying last, being connected to the latter through ductshaving a relatively large cross-sectional area, thus being able topost-feed these parts with liquid metal to compensate for thecontraction.

Such post-feeding reservoirs are mainly known in two forms, viz. asfeeders or risers, i.e. substantially cylindrical cavities leading fromthe duct connecting them to the casting to the upper surface of themould, or in the form of internal or closed cavities in the mould,so-called “blind feeders” or “shrinkage knobs” placed in the immediatevicinity of the part of the casting to be post-fed. Compared to thelatter type, the former presents the advantage that the highestmetallostatic pressure at the feeding location, i.e. the pressure fromthe superjacent metal column, to a high degree assists the feeding bypressing the feeding metal through the connecting duct into the casting,in contrast to which the pressure in the latter type diminishes duringthe feeding process. On the other hand, the latter type presents theadvantage of normally producing a higher yield of metal in the castingprocess, i.e. a lesser quantity of metal to be separated from thecasting after the casting process for subsequent re-melting(re-circulation), which also reduces the energy used for melting.

When risers or “shrinkage knobs” connected to the mould cavity properare used, they are conventionally filled with melt having been cooledduring the pouring process, which is especially the case with bottompouring. For this reason, these cavities constituting the post-feedingreservoirs must be made sufficiently large to ensure that—in spite ofthe cooling—liquid melt is still present in the reservoir forpost-feeding when the casting solidifies. The result of this can bethat, when using certain alloys or when producing critical castings, ayield of only approximately 50% can be achieved, i.e. that after thecasting, the post-feeders and the ingate system weigh the same as thecasting to be produced. The amount of material thus being necessary tomelt in addition to what is used for the desired casting itselfconstitutes an energy loss, increasing the cost of the casting processand at the same time necessitating a higher melting capacity for thefoundry equipment.

Some of these disadvantages can be avoided by constructing and using theingate system as a post-feeding means, to this end comprisingpost-feeding cavities. In this manner, a post-feeding reservoir isobtained that is heated by the melt on the latter's passage to the mouldcavity. Optimally, this post-feeding reservoir must be constructed tohave the least possible heat loss, so that the least possible quantityof melt is used for heating the reservoir and maintaining it hot so asto maintain the melt in it in the liquid state. The least possible heatloss is i.a. achieved by constructing the reservoir with the leastpossible surface area per unit of heat. Further, the heat loss isminimized during the post-feeding process by placing the reservoir closeto the mould cavity. The total result of this is that such post-feedingreservoirs, in consideration of the heat loss, are optimally constructedas cavities constituting a large widened part of the ingate systemimmediately upstream of the inlet to the mould cavity. When using bottomingates, this does, however, give rise to the disadvantage that thebottom ingate must be shaped and arranged in such a manner that it willnot be blocked by solidified melt until the casting itself is solidifiedto such a degree that post-feeding is no longer necessary.

From DE-36 21 334 it is known to use a movable tube for pouring. Thepost-feeding is provided by a riser positioned at the top of the castingcavity.

DE-34 44 941 shows another possibility using a movable tube for pouring.The post-feeding is provided from a post-feeding reservoir at the sideof the casting cavity, said reservoir being connected to the castingcavity at the bottom via the ingate, which means that the post-feedingis performed through the bottom-filling inlet to the casting cavity,whereby said bottom-filling inlet will have to be constructed in such amanner that it will not be blocked by solidified melt until the castingitself is solidified to such a degree that post-feeding is no longernecessary.

DISCLOSURE OF THE INVENTION

It is, on this background, the object of the present invention toprovide a method and casting mould of the kind referred to initially,with which it can be achieved

that the inlet from the post-feeding reservoir is not blocked bysolidified material before the casting itself has solidified to a degreenot necessitating additional post-feeding,

that the surplus material to be removed after the casting process iskept at the lowest level possible,

that the ingate system, including the post-feeding reservoir, occupiesthe least possible space in the mould, and

that the position of the post-feeding can be selected more freely.

This object is achieved with a method of the kind referred to initially,being characterized by the use of an ingate system comprising adownsprue extending downward from an inlet to an outlet communicatingwith the bottom ingate of the casting cavity and connecting to a feedingreservoir through flow-restricting means, from which feeding reservoir afeeding duct extends to a location in the side of the casting cavity atleast approximately at the same level as the level of the region ofreduced pressure in the casting cavity in which the solidification canbe expected to take place last.

The invention is based upon the fact that, when the post-feeding takesplace through a duct debouching close to the place, where thesolidification—on the basis of experience and/or calculations—can beexpected to take place last, also called the thermal centre of gravityfor the casting, the un-solidified melt in the casting and thepost-feeding reservoir co-operate to keep the post-feeding inlet ductopen, providing the advantage that it is not necessary to use melt forfilling a bottom ingate system and keep the latter heated, making itpossible to arrange and construct the bottom ingate system primarilywith regard to the flow conditions and minimized material consumptionand to a lesser degree in consideration of late solidification. Further,the column of melt and the pressure connected to and possibly applied tosame may post-feed melt to the mould cavity during the post-feedingprocess with a minimum of friction.

The present invention also relates to a casting mould or mould part foruse when carrying out the method according to the invention. Thiscasting mould or mould part is of the kind set forth above and in detailhereinbelow.

Additional advantageous embodiments of the method and the casting mouldor mould part, the effects of which—beyond what is obvious—are explainedin the following detailed part of the present description.

BRIEF DESCRIPTION OF THE DRAWINGS

In the following detailed portion of the present description, theinvention will be explained in more detail with reference to thedrawing, in which

FIG. 1 is a front view of an ingate system for use in a firstembodiment,

FIGS. 2a-e show side views of the ingate system according to FIG. 1 invarious degrees of filling,

FIG. 3 is a top view showing in cross-section the downsprue shown inFIG. 1 with post-feeding reservoir, gauze screen and downsprue,

FIG. 4 shows in cross-section at an enlarged scale the downsprue with aninsulating layer around the post-feeding reservoir shown in FIG. 3,

FIG. 4a is a cross-section of the downsprue at an enlarged scale, inwhich the gauze screen surrounds the downsprue,

FIG. 4b is a cross-section of the downsprue at an enlarged scale, inwhich the gauze screen forms the downsprue within the post-feedingreservoir,

FIG. 5 shows an example of pouring when using the ingate system of FIGS.1-4 as viewed in section through a mould,

FIG. 6 shows a string-moulding plant, in which the ingate systemaccording to the invention can be used, and which serves to illustratethe process,

FIGS. 7a-e show an ingate system according to the invention, shown inthe same manner as in FIG. 2, and

FIG. 8 shows an example of pouring in a similar manner as shown in FIG.5, but according to the invention with separate post-feeding inlet,while

FIGS. 9 and 10 show an example of pouring according to the invention byusing a movable tube.

DESCRIPTION OF THE PREFERRED EMBODIMENTS

FIG. 1 shows an ingate system 1 consisting of a pouring cup 2, a meltrunner 3, a downsprue 4 and an inlet 5. In this ingate system, a meltrunner 3 is placed downstream of the pouring cup in order to ensure thatthe melt will not be poured directly down into the downsprue 4, so thatthe melt will arrive in a calm state at the entrance to the downsprue 4,in the drawing shown as extending vertically. Then, the melt flows fromthe downsprue top 4 a to the downsprue bottom 4 b. In the embodimentshown, the downsprue 4 is shaped like a flat duct which, as will be seenfrom FIGS. 3 and 4, converges downwardly. The flat-duct shape of thedownsprue 4 ensures that the flow in the downsprue 4 can take placesubstantially laminarly without turbulence.

The shape of the downsprue 4, converging downwardly towards the bottom 4b, ensures that low pressure does not arise in the top 4 a of thedownsprue 4, especially during the initial phase of the pouring of themelt, as a correctly converging shape ensures the same static pressureat the top 4 a as at the bottom 4 b.

A straight or non-convergent downsprue 4 would cause the “pull” from themelt column to produce a lower pressure at the top 4 a than at thebottom 4 b, there being no back pressure from melt in the mould cavity15 capable of acting in the opposite direction through the ingate system1. Thus, with this converging shape of the downsprue 4, commonly knownto persons skilled within this art, it is possible to ensure a uniformpressure throughout the downsprue 4, when the latter is shaped inconsideration of Bemoulli's equations relating to velocity, height andpressure.

One side of the downsprue 4 is in the form of a gauze screen 6separating a feeding reservoir 7 from the downsprue 4 proper. The gauzescreen 6 is permeable to the melt, but offers resistance against suchpenetration. When, in the initial phase of the pouring, a uniformpressure is being built up in the downsprue 4, this pressure alsoreigning in the feeding reservoir 7, the gauze screen 6 will, because ofits resistance to flow through it, act in the manner of an ordinary ductwall. For this reason, the melt flows in the downsprue 4 proper and doesnot to any significant extent penetrate into the feeding reservoir 7.The feeding reservoir 7 is, however, heated, at least with radiant heatfrom the melt flowing through the downsprue 4. As the melt in the mouldcavity 15 gradually builds up a back pressure in the downsprue bottom 4b, the pressure in the latter will rise, causing melt to penetratethrough the gauze screen 6 into the feeding reservoir 7, in which aprocess of slow filling is initiated. This will continue, the gauzescreen 6 still, however, offering a certain resistance againstpenetration by the melt. When after this, the mould cavity 15 has beenfilled with melt right up to the top, the liquid flow through thedownsprue 4 ceases, and the full pressure from the melt being poured isnow applied via the gauze screen 6 to the reservoir 7, the latter thenbeing filled quickly.

After this, the pouring in the pouring station, indicated with B in FIG.6, ceases, and if the mould is a mould 14 in a string of moulds, it canpass on in the direction of the arrow A to the cooling zone C.

In the cooling zone C, the casting contracts during solidification inthe mould cavity 15, resulting in a fall of pressure in the ingatesystem 1, causing melt to be drawn from the feeding reservoir 7 to fillthe cavities produced by the contraction in the mould cavity 15.

FIG. 5 shows a mould with a bottom inlet comprising an inlet duct 5 aand an ingate 5 b, using an ingate system 1 as shown in FIG. 1. Whenmelt is poured from a pouring device 17 into the pouring cup 2, the meltwill flow on via the ingate system 1 to the mould cavity 15, the meltascending through the latter. In FIG. 5, the mould cavity 15 is shown asterminated upwardly by a riser 16, the latter, however, not beingabsolutely necessary.

As shown in FIG. 6, the mould 14 can be produced in a moulding machine10, in which mould sand from a supply reservoir 11 is made to run into amoulding space, in which patterns 13 a, 13 b on a hydraulic piston 12and a counter-pressure plate 13 c, respectively, are pressed againsteach other so as to form a mould 14, the latter then being pushed outinto the string of moulds by the hydraulic piston 12 so as to form apart of the string of moulds. The mould is pushed further to a pouringstation B, in which the mould cavity is filled with melt. After this,the mould 14 is moved further in the direction of the arrow A to acooling zone C, in which the melt solidifies and the casting contracts.

The course of events in the ingate system 1 during this casting process,e.g. in a moulding plant as shown in FIG. 6, is shown in FIG. 2 withFIGS. 2b-2 e. Of these, FIG. 2b shows the initial phase of the pouring,during which the ingate system has just been filled up, and FIG. 2cshows the situation, in which the back pressure from the melt in themould causes melt to penetrate into the feeding reservoir 7. When thehydraulic pouring surge occurs as a result of the mould cavity havingbeen completely filled, the feeding reservoir is substantiallycompletely filled as shown in FIG. 2d. When, after this, the castingcontracts, melt will be drawn from the feeding reservoir 7, as indicatedin FIG. 2e.

When moulds are being produced in a moulding plant of the kind shown inFIG. 6, the feeding reservoir 7 and the gauze screen 6 can,advantageously be manufactured and inserted in the form of aprefabricated integrated unit, possibly being insulated with aninsulating tube 8.

The gauze screen 6 can e.g. be produced from a material consisting ofquartz glass in thin fibres, assembled to form a web with square holesbonded with a resin, but the gauze screen may, of course, also bemanufactured from other materials that are heat-resistant, e.g. ordinaryglass-fibre web.

The permeable wall may be in other forms than a gauze screen; it maye.g. be in the form of a perforated plate, a grate, a sieve or screenetc., e.g. perforations in an insulating tube.

The shape of the duct, in which the feeding reservoir 7 and the gauzescreen 6 are situated, may, of course, differ from that shown; it cane.g. be a more or less horizontal canal or duct, in which the gauzescreen 6 constitutes the upper side.

Further, the downsprue 4 and the feeding reservoir 7 as such may alsohave a shape other than that shown, taking into consideration, however,that the flow must be at least substantially laminar, and that it isnecessary as explained above to avoid low pressure in the duct system.

FIG. 4a shows an embodiment, in which the gauze screen 6 surrounds thedownsprue 4. With this arrangement, one side of the gauze screen 6functions as a permeable wall, while its remaining sides function tostrengthen the duct. With this arrangement, the duct 4, 5, 5 a and 5 bmay be in the form of pre-fabricated hollow-profile elements to beinserted as individual units or integrated with the feeding reservoir 7prior to insertion, or else assembled from two parts each inserted in arespective mould 14.

An especially advantageous construction with pre-fabricated ducts 4 canbe achieved, when the latter is inserted in the feeding reservoir 7, andwhen the latter or parts thereof constitute the duct walls or duct unitsin the manner indicated in FIG. 4b.

This construction makes it i.a. possible to construct the reservoir 7with a spherical shape and to let the inlet/downsprue 4 extendtransversely through the reservoir whilst maintaining a substantiallylaminar flow, at the same time as the reservoir 7 has a small surfacearea and hence a low heat loss due to the spherical or cylindricalshape. Further, in this case, all the duct walls are heated by thereservoir 7, and solidification at the walls during the feeding processis avoided.

When the feeding reservoir 7 and the gauze screen 6 are constructed inthe form of an integrated unit, this unit can advantageously beprefabricated and inserted during the making of the mould 14.

Further, the feeding reservoir 7 can be provided with means formaintaining the pressure and/or keeping the feeding reservoir 7 underpressure, also when the latter leaves a pouring station, and suchpressure-generating means may e.g. be provided in the manner indicatedin the International Application No. WO 95/18689.

When used with pouring from the bottom (ascending casting), therequirements to the feeding reservoir 7 are

the least possible influence on the flow conditions,

that the feeding reservoir 7 and the duct system leading from it to themould cavity 15 are so constructed that they will not be blocked by meltsolidifying before the feeding process is complete,

that it is capable of delivering melt to regions in which contractiontakes place, and

that the size of the ingate system including the feeding reservoir 7,later to be removed from the finished cast article, is as small aspossible.

Because the castings as such have what could be called a thermal centreof gravity, usually lying centrally in the casting, i.e. above thebottom ingate, and the latter itself lies close to the outside of themould, i.e. being well cooled, it is necessary to influence theserelations when constructing the ingate system when the feeding reservoiris to be situated in it. To begin with, the flow of all the melt intothe mould cavity 15 contributes towards heating the bottom to a highertemperature and thus moving the thermal centre of gravity for thecasting in a downward direction.

This is, however, insufficient, because the bottom cooling will move thethermal centre of gravity upwardly in the mould cavity, and for thisreason, the bottom ingate system must be made of such a size andpossibly thermally insulated in such a manner, that the thermal centreof gravity is held closer to the bottom ingate. All this makes theingate system larger and more complicated.

According to the present invention, these problems are overcome byproviding a separate feeding duct from the feeding reservoir 7 to themould cavity 15 at the latter's thermal centre of gravity.

This feeding duct is so arranged, that it does not establish aconnection between the melt in the feeding reservoir and the melt in themould cavity until the level of melt in the mould cavity has reached thelevel of the feeding duct or later.

In the embodiment shown in FIGS. 7 and 8 this takes place by a feedingreservoir 7 being gradually filled concurrently with the filling of themould cavity 15. As shown in FIG. 7, the reservoir 7 is filled graduallywhile the mould cavity 15 is being filled, and when the level of melt inthe feeding reservoir 7 reaches the level of the feeding duct 21, themelt will begin to flow through the latter into the mould cavity 15.

The feeding duct 21 and the feeding reservoir 7 are so constructed andarranged, that the melt does not flow into the mould cavity 15 until ithas penetrated from the bottom ingate 5 and upwards in the mould cavity15 to a level at least as high as the outlet from the feeding duct 21.When the melt has penetrated into the mould cavity 15 via the feedingduct 21, the latter becomes an active component of the ingate system, sothat melt is supplied to the mould cavity 15 via the bottom ingate 5 andthe feeding duct 21. After this, the supply of melt via the bottomingate 5 is not strictly necessary, for which reason this ingate ismerely arranged to be capable of fulfilling its normal function as abottom ingate. This means that the bottom ingate 5 is much smaller thanif it were also to constitute a feeding duct, possibly without heatinsulation.

During this latter part of the normal mould-filling process, the melthaving flowed through the feeding duct 21 has heated the latter, andafter this, the liquid melt in the heated feeding duct 21 is subjectedto a pressure from the melt in the feeding reservoir 7. During thesubsequent contraction of the casting in the mould cavity melt forfeeding is supplied to the mould cavity 15 via the feeding duct 21.

Thus, with this arrangement it is not necessary to keep the melt in theliquid state in the bottom ingate system proper for feeding purposes.Further, it is possible to deliver the melt during the feeding processclose to the thermal centre of gravity for the casting in the mouldcavity 15, so that the heating is facilitated, because parts of thecasting undergoing contraction will first pull feeding melt from regionsclose to the thermal centre of gravity at the same time as the latter isfed with melt via the feeding duct 21. This process reduces thefrictional resistance against the feeding melt, as the latter does nothave to pass previously solidified melt, and the risk of solidified meltinterrupting the feeding process before its completion is avoided.

Thus, with this arrangement it is unnecessary to keep the melt in theliquid state in the ingate system below the feeding reservoir 7 and thefeeding duct 21, and this reduces the consumption of material in theform of melt and makes it possible to construct the mould in a morecompact manner, including the omission of any thermal insulation of thebottom ingate 5. Further, it is not necessary to lower the thermalcentre of gravity towards the bottom ingate by means of a large mass ofmelt and/or insulation in order to keep the bottom ingate free forfeeding purposes.

The feeding duct 21 itself can be given any desired shape, and may e.g.be inclined in order to adapt the filling of the feeding reservoir 7 tothe filling of the mould cavity 15, or it may be made to constitute apart of the vertical extent of the feeding-melt column.

The feeding duct 21 can advantageously be thermally insulated, and maypossibly be pre-fabricated, e.g. together with the feeding reservoir 7in materials similar to the latter, and be inserted in a mannercorresponding to what has been explained above.

In a second embodiment shown in FIGS. 9 and 10, the bottom ingate isreplaced by a pouring tube 23, which at the start of the pouring hasbeen introduced through the pouring inlet 4, and the feeding duct 21 hasbeen replaced by a feeding duct 24, 25 (of which the lower part 24corresponds to the feeding duct 21 from the feeding reservoir 7 in theprevious exemplary embodiment) to the bottom of the mould cavity 15.When pouring has begun, the melt is poured through a funnel 22 and thepouring tube 23 to the bottom of the mould cavity 15, and at the sametime as the level of melt in the mould cavity 15 ascends, or before themelt has solidified, the pouring tube 23 is pulled up from the bottom ofthe mould cavity 15 and away from the latter through the feeding duct24, 25, during which process the latter's lower part 24, nowconstituting a feeding reservoir, is filled.

The pouring tube 23 is made from heat-resistant material capable ofwithstanding the heat encountered during the pouring, and it canadvantageously be constructed with a cross-sectional shape ensuring alaminar flow, possibly also converging downwardly as described above, ifthis is desirable.

The latter arrangement makes it possible to carry out ascending castingunder increased pressure without risk of damage to the ingate system orany need of constructing the latter in a special manner with a view tobeing able to withstand this increased pressure.

Thus, taken as a whole, the invention makes it possible to achieve asaving in material, partly with regard to melt required for pouring,partly with regard to mould-making material for making a mould that cannow be made smaller. Further, the quality of the finished casting isimproved because the feeding is more effective and certain, when thefeeding takes place via a feeding reservoir in the ingate system havingbeen pre-heated by the melt being poured in and debouches close to thethermal centre of gravity for the casting. In addition to this, thequality of the finished casting is improved even more, either by shapingthe bottom ingate primarily with a view to good flow conditions, or byomitting the bottom ingate, making it possible to ensure good flowconditions by means of the pouring tube being inserted.

LIST OF PARTS

A arrow

B pouring station

C cooling zone

1 ingate system

2 pouring cup

3 melt runner

4 downsprue/duct/pouring inlet

4 a downsprue top

4 b downsprue bottom

5 bottom ingate

5 a inlet duct

5 b ingate

6 gauze screen

7 feeding reservoir

8 insulating tube

10 moulding machine

11 supply reservoir

12 hydraulic piston

13 a pattern

13 b pattern

13 c counter-pressure plate

14 mould

15 mould cavity

16 riser

17 pouring device

21 feeding duct

22 funnel

23 pouring tube

24 feeding duct, lower part

25 feeding duct, upper part

What is claimed is:
 1. A method of ascending casting of an article froma molten material poured initially into a bottom of a casting cavitywhere, during cooling of the molten material, a region of reducedpressure forms at which region solidification of the molten material islast expected to take place, said method comprising the steps of:providing an ingate system having a downsprue, the downsprue extendingdownward from an inlet to an outlet communicating with a bottom ingateof the casting cavity; providing a feeding reservoir which connects tothe casting cavity through a feeding duct separate from the bottomingate, the feeding duct extending from the feeding reservoir to alocation in a side of the casting cavity at a level of the castingcavity approximately equal to a level of the region of reduced pressure;separating the feeding reservoir from the downsprue with a flowrestricting mechanism, the flow restricting mechanism acting as abarrier to flow and allowing flow of the molten material directly fromthe downsprue to the feeding reservoir when a sufficient back pressureof the molten material occurs in a bottom of the downsprue as the moltenmaterial fills the casting cavity; pouring molten material into thedownsprue of the ingate system such that the feeding reservoir is filledwith molten material directly from the downsprue at an ascending levelat least no higher than an ascending level of the molten material in thecasting cavity; and cooling of the molten material of the casting, saidcooling step including feeding of make-up molten material to the coolingcasting through the feeding duct from the feeding reservoir and in turndirectly from the downsprue.
 2. A method of ascending casting as claimedin claim 1: wherein the ingate system providing step includes providingthe downsprue with a length; wherein the feeding reservoir providingstep includes extending the feeding reservoir adjacently along asubstantial length of the length of the downsprue; and wherein theseparating step includes providing of the flow restricting mechanism asa melt permeable wall along the substantial length of the feedingreservoir between the feeding reservoir and the downsprue.
 3. A methodof ascending casting as claimed in claim 2, wherein the pouring stepincludes restricting of the flow of molten material through the flowrestricting mechanism into the feeding reservoir until the castingcavity is substantially filled with molten material.
 4. A method ofascending casting as claimed in claim 2, wherein the pouring stepincludes restricting of the flow of molten material through the flowrestricting mechanism into the feeding reservoir such that the ascendinglevel in the feeding reservoir approximates the ascending level in thecasting cavity.
 5. A method of ascending casting as claimed in claim 2,wherein the feeding reservoir providing step includes extending thefeeding reservoir to the outlet of the downsprue.
 6. A casting mouldused for ascending casting of an article from a molten material where,during cooling of the molten material, a region of reduced pressureforms at which region solidification of the molten material is lastexpected to take place, said casting mould comprising: a casting cavityhaving a bottom into which the molten material is initially poured and apredetermined level of the region at which solidification is expected totake place last; and an ingate system which supplies molten material tothe casting cavity, said ingate system including (a) a feeding ducthaving a lower part which debouches at the location in the side of thecasting cavity approximately at the predetermined level of the region ofreduced pressure, and (b) a pouring tube extending through the feedingduct and having (a) an upper inlet and (b) an outlet at a lowermost endthereof, said pouring tube being movable through said feeding duct in alongitudinal direction of said feeding duct between a pouring positionin which said outlet is located close to the bottom of said castingcavity and a feeding position in which said outlet is situated at leastat the level of said casting cavity approximately equal to thepredetermined level of the region of reduced pressure.
 7. A method ofascending casting of an article from a molten material poured initiallyinto a bottom of a casting cavity where, during cooling of the moltenmaterial, a region of reduced pressure forms at which regionsolidification of the molten material is last expected to take place,said method comprising the steps of: providing an ingate system for thecasting cavity which includes a feeding duct having a lower part whichdebouches at a location in a side of the casting cavity approximately ata level of the region of reduced pressure; initially pouring moltenmaterial into the casting cavity from a pouring tube in a pouringposition, the pouring tube extending through the feeding duct and having(a) an upper funnel and (b) an outlet at a lower end thereof locatedclose to the bottom of the casting cavity; and subsequently moving,substantially not later than when filling of the casting cavity iscompleted, the pouring tube longitudinally in the feeding duct to afeeding position for molten material at which feeding position theoutlet of the pouring tube is situated at least at a same level as thelocation in the side of the casting cavity.
 8. A method of ascendingcasting of an article as claimed in claim 7 wherein said moving stepincludes the step of moving the outlet so as to substantially follow arise of a level of the molten material in the casting mould.
 9. Acasting mould used for ascending casting of an article from a moltenmaterial where, during cooling of the molten material, a region ofreduced pressure forms at which region solidification of the moltenmaterial is last expected to take place, said casting mould comprising:a casting cavity having a bottom into which the molten material isinitially poured through a bottom ingate and a predetermined level ofthe region at which solidification is expected to take place last; aningate system which supplies molten material to the casting cavity, saidingate system including a downsprue extending downward from an inlet toan outlet communicating with said bottom ingate of the casting cavity; afeeding reservoir for the casting cavity, said feeding reservoir beingconnected by a feeding duct to a location in a side of said castingcavity at a level approximately equal to the predetermined level of theregion of the casting cavity; and a flow-restricting mechanism whichseparates the feeding reservoir from the downsprue, said flowrestricting mechanism acting as a barrier to flow and allowing flow ofthe molten material directly from the downsprue to the feeding reservoirwhen a sufficient back pressure of the molten material occurs in abottom of the downsprue as the molten material fills the casting cavitysuch that said feeding reservoir is filled with molten material directlyfrom said downsprue to an ascending level at least no higher than anascending level of the molten material in said casting cavity, and suchthat during cooling of the molten material of the casting make-up moltenmaterial for the cooling casting is drawn through said feeding duct fromsaid feeding reservoir and said downsprue.
 10. A casting mould asclaimed in claim 9: wherein said downsprue has a length; wherein saidfeeding reservoir extends adjacently along a substantial length of thelength of said downsprue; and wherein said flow restricting mechanismforms a melt permeable wall along the substantial length of said feedingreservoir between said feeding reservoir and said downsprue.
 11. Acasting mould as claimed in claim 10, wherein said flow restrictingmechanism restricts flow of the molten material into said feedingreservoir until said casting cavity is substantially filled with moltenmaterial.
 12. A casting mould as claimed in claim 10, wherein said flowrestricting mechanism restricts flow of the molten material into saidfeeding reservoir such that the ascending level in said feedingreservoir approximates the ascending level in said casting cavity.
 13. Acasting mould as claimed in claim 10, wherein said feeding reservoir andsaid flow restricting mechanism extend upwardly from said outlet of saiddownsprue.